I4 WATER FOR INDUSTRIAL PURPOSES
ence of a few drops of methyl orange solution until a faint red coloration
(similar to that given by methyl orange with a saturated solution of carbon
dioxide in distilled water) is obtained. The result is expressed in grams
of CaC03 per litre of the water; using 200 c.c. of the water, each i c.c.
of the N/5-HC1 corresponds with 0-05 gram of CaCO-, per litre.
When the water contains sodium carbonate—which is the case, not
with ordinary natural waters, but only with certain mineral waters and
with waters treated with sodium carbonate—it is necessary to boil a given
volume of the water (gradually replacing that which evaporates) until
the bicarbonates are decomposed, and then to filter and determine the
alkalimetric titre of the filtrate. This alkalinity represents the sodium
carbonate existing in the water, together with those minute quantities of
the alkaline earth carbonates which remain dissolved (0-036 gram of CaC03
and o-i gram of MgC03 per litre).1
2. Determination of the Lime and Magnesia. Two hundred
c.c. of the water are boiled for some minutes with excess of sodium carbonate
solution in a porcelain dish and then evaporated to dryness. The residue
is heated at 180° and treated with boiling water, the liquid being filtered
and the precipitated alkaline earth carbonates washed with a little boiled
water and dissolved in excess of N/5-hydrochloric acid. Tim excess of add
is then titrated with. N/5-caustic soda, solution in presence of methyl orange.
In this case, lime and magnesia, are calculated together as Cat); when
200 c.c. of the water are taken, each c.c. of N/5-HC1 used corresponds with
0-028 gram of CaO per litre of the water.-
3. Estimation of Sulphates .-—To 200 c.c. of the water, acidified with
a little hydrochloric acid, barium chloride; is added ; if an appreciable
precipitate forms after some hours, the sulphuric acid is estimated in the
usual way (sec Potable Waters : Complete? Analysis, 4), The sulphuric
acid found may be calculated as CaSO,,; i part of 'F»a,S()a corresponds
with 0-5827 part of CaSO,,.
4. Other Tests.......-Where qualitative analysis shows the presence of
marked quantities of magnesia, it is well to determine this gravimetneully, the
lime being first eliminated by means of ammonium oxalate and the mag-
nesia then precipitated with sodium phosphate and weighed as magnesium
pyrophosphate in the ordinary way. i
When an appreciable amount of chlorides is indicated qualitatively, the
chlorine is determined (sec Potable Waters : Complete Analysis, 3) and
calculated as NaCl.
Also, if qualitative analysis reveals the presence of iron, this may be
determined gravimetric-ally or colorimetrically by Lunge's method (see
5. Calculation of the Results.—The lime (CaO) corresponding with
the calcium sulphate found according to 3 is subtracted from the total
lime found according to 2; the difference will represent the lime in the
1 The alkalinity of a water for industrial uses may also be determined "by the method
indicated for Potable Waters: Partial Analysis, 3.
2 With waters rich in magnesia it is convenient to follow the method proposed by
Wartha and Pfeifer (Zeitschr. /. angew. chem., 1902, p. 193) or that of Gigli (seep. $), taken for the titration of the excess of silver. ~, (.